Red hair inherits recessively via R151C, R160W, D294H, R142H, 86insA, 537insC alleles. V60L variant acts as partially penetrant recessive allele. Heterozygotes for R151C or 537insC face significantly elevated red hair risk. Heterozygotes show different red hair shade than homozygotes or compound heterozygotes. Heterozygotes exhibit effects on beard hair color, skin type, and freckling. MC1R variants produce dosage effects on hair and skin color. Study covers 174 individuals from red hair kindreds plus 99 unrelated redheads and 167 random Caucasians. Variants common in Caucasian populations. Red hair phenotype confirmed recessive in most cases.